1. Field of the Invention
The present invention relates to a method and an apparatus for preventing undesirable cooling particularly at the strip edge areas of a cast strand by means of the running water which emerges from the bottom opening of a secondary cooling chamber.
2. Description of the Related Art
In the operation of continuous casting plants for thin slabs it is known that running water emerges laterally next to the strand where the strand exits the secondary cooling chamber; this causes an undesired intensive undercooling of the strand edges. This effect is intensified as the casting size increases and as the casting speed increases.
In a continuous casting plant according to DE-OS 2 208 928, in which the strand is continuously pulled downwardly out of a water-cooled mold and is guided through a supporting and guiding device with rollers, a portion of the cooling device is formed by fan jet nozzles which are arranged parallel to the surface of the strand, i.e., parallel to the long side of the slab and at a distance therefrom, wherein the longitudinal axis of the cooling device extends parallel to the axes of the rollers. Moreover, in accordance with the known continuous casting plant, the fan jet nozzles are arranged in the area of a slab edge and are preferably arranged at both slab edges opposite each other and offset relative to each other.
In this known continuous casting plant with an arch-shaped supporting and guiding device for guiding the strand from an essentially vertical direction into an essentially horizontal direction, the cooling device is composed of fan jet nozzles in the area of deflection of the strand, i.e., along approximately ⅓ to ⅔ of the length of the supporting and guiding device. In particular, the cooling device is also at the bottom side of the slab composed of fan jet nozzles.
DE-AS 1 558 194 describes a method and an apparatus for cooling a cast strand in a secondary cooling zone. The cast strand is cooled in zones which are offset relative to each other transversely of the strand axis, such that the cooling effects in the zones of adjacent planes supplement each other over the strand surface transversely of the strand axis so as to achieve an approximately uniformly extending cooling effect.
DE-AS 1 289 956 discloses a secondary cooling device for continuous casting products with straight or flat surfaces. This cooling device is composed of a plurality of spray or dispersion nozzles arranged transversely of the strand axis. The spray nozzles have a flat characteristic of the impinging quantity of cooling medium and are arranged at such a distance from each adjacent nozzle that the nozzle sides overlap each other to such an extent that the cooling effect in the overlapping portion deviates only slightly from the cooling effect of the surface portions located outside of the overlapping portions.
None of the devices known in the art include effective means for preventing the running water from emerging laterally next to the strand and the attendant undesirable intensive cooling of the strip edge areas.
Staring from the prior art discussed above, it is the primary object of the present invention to provide a method and an apparatus for carrying out the method in which the emergence of running water from the secondary cooling chamber of a continuous casting plant laterally next to the strand and the attendant undesirable intensive undercooling of the strip edges are prevented.
In accordance with the present invention, in a method and an apparatus of the above-described type, high-energy spray jets of a deflection medium are produced and are directed preferably transversely of the strip edge areas against the running water outlet, such that the running water is deflected from the strip edge areas and is discharged through outlet openings of the secondary cooling chamber provided on both sides of the cast strand.
The solution according to the present invention of the object described above provides the advantage that an undesirable intensive cooling of the strip edge areas by the running water is suppressed.
By adjusting the process parameters, for example, adjustment of direction, energy content and number and throughput quantity of the individual nozzles, the effectiveness of the method according to the invention is optimized to the required extent and the existing conditions of the strand production of a thin slab casting plant are taken into consideration in an optimum manner.
In accordance with a further development of the method according to the invention, water or air or a water/air mixture are used as the deflect ion medium. This results in an even better adjustment of the process parameters to the existing production condition of a continuous casting plant.
The method according to the present invention further provides that spray jets with flat spray cones are produced. A spray jet of this configuration removes a minimum of heat from the strand, although it cannot be avoided that the deflection medium is also Partially sprayed onto the strand.
In accordance with another further development of the method according to the invention, partially overlapping rows of spraying cones are produced transversely on each side of an edge of the cast strand. This ensures that each side of an edge of the cast strand is completely covered with spray jets of the deflection medium.
In accordance with another further development of the method of the invention, the spray jets are sprayed preferably at an angle a against the travel direction of the running water. As a result, the deflection of the running water is optimized because the nozzles spray upwardly against the direction of flow of the running water.
In accordance with another advantageous embodiment of the invention, the deflection medium is sprayed against the edge areas of the cast strand at a relatively small distance upstream of the bottom opening of the secondary cooling chamber. This results in especially favorable process parameters for the deflection of the running water from the strip edge areas.
In accordance with another embodiment of the invention, several nozzles are arranged in a row so as to extend over the width of the strand, wherein individual pairs of nozzles of the rows of nozzles can be switched on or off depending on the changing width of the strand. This is an uncomplicated and advantageous way to provide changeable zones of strip edge areas to be sprayed transversely of the strand axis depending on the respective width of the strand.
Finally, the invention provides that the spray jets are sprayed essentially perpendicularly relative to the surface of the strip edge areas. This results in an optimum blocking effect of the emerging running water without the long sides of the strand being impinged in an undesired manner by the spray jets so that the strand edges are not subjected to an undesired cooling effect.
An apparatus for preventing an undesirable intensive cooling of the strip edge areas of a cast strand by the running water emerging from the bottom opening of a secondary chamber includes spray nozzles arranged in a row for producing high-energy spray jets directed against the running water outlet, wherein the spray nozzles are arranged at a relatively small distance upstream of the bottom opening of the secondary cooling chamber for the cast strand, and wherein the spray nozzles are combined in rows extending in the direction of the strand width and the spray nozzles are connected individually through throttle means to a feed line.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.